The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

2018 Equinox P0420 Code - Catalyst System Efficiency Below Threshold

0

Mike T. · rep 0 · May 25, 1:38 AM · 1 replies · solved · Question

Vehicle: 2018 Chevrolet Equinox LT

Hey everyone,

My 2018 Chevrolet Equinox LT, with about 85,000 miles, just threw a Check Engine Light. I used my basic OBD-II scanner and it's showing a P0420 code: Catalyst System Efficiency Below Threshold (Bank 1).

The car seems to be driving fine, no noticeable loss of power or strange noises. Fuel economy hasn't taken a huge hit either, at least not that I can tell immediately.

What are the common causes for this code on an Equinox of this year? Is it definitely a bad catalytic converter, or could it be something simpler like an O2 sensor? Any advice on how to diagnose this further before I take it to a shop would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:38 AM

0

ClearTheCode admin answer:

The P0420 code on your 2018 Chevrolet Equinox LT indicates that the catalytic converter on Bank 1 is not performing as efficiently as it should. While a failing catalytic converter is a possibility, it's crucial to rule out other causes first. Here's a breakdown:

Common Causes:

  1. Failing Oxygen Sensors: The upstream (pre-cat) and downstream (post-cat) O2 sensors work together to monitor catalyst efficiency. A faulty downstream O2 sensor can falsely trigger a P0420 code, or a failing upstream sensor can cause the engine to run rich/lean, damaging the converter.
  2. Exhaust Leaks: Leaks in the exhaust system before or near the catalytic converter can allow unmetered air in, affecting O2 sensor readings and tricking the ECU into thinking the converter is inefficient.
  3. Engine Misfires or Rich/Lean Conditions: Persistent misfires, fuel injector issues, or other engine problems that cause excessive unburnt fuel or too much oxygen to enter the exhaust can damage the catalytic converter over time.
  4. Contaminated Catalytic Converter: Antifreeze or oil entering the exhaust system (due to head gasket issues, piston ring wear, etc.) can contaminate the catalyst, reducing its efficiency.
  5. Failing Catalytic Converter: Over time, the catalyst material can degrade, especially if exposed to the conditions listed above.

Diagnostic Steps:

  1. Check for Exhaust Leaks: Visually inspect the exhaust system for any cracks, holes, or loose connections, especially around the manifold and converter.
  2. Scan for Other Codes: Use a more advanced scanner if possible to check for any pending or historical codes that might point to misfires (P030x), O2 sensor issues (P013x, P014x), or fuel trim problems (P0171, P0172).
  3. Monitor O2 Sensor Data: If your scanner allows, monitor live data for the upstream and downstream O2 sensors. The upstream sensor should fluctuate rapidly, while the downstream sensor should show a relatively steady voltage. If the downstream sensor mirrors the upstream, it indicates an inefficient catalytic converter.
  4. Inspect Spark Plugs/Ignition System: Ensure the engine is running smoothly without misfires.

When to See a Shop:

  • If you've performed the basic checks and can't pinpoint the issue.
  • If the code returns immediately after clearing, especially if accompanied by poor performance.
  • If you suspect an exhaust leak that's difficult to locate.
  • If O2 sensor data confirms a failing catalytic converter, as replacement is a significant job requiring specialized tools.
Menu

Help & account